Yaojie Fm
Type Locality and Naming
It was named by Sun Jianchu as the Yaojie System in 1936. The naming section is located in the Yaojie area of the Honggu District, Lanzhou City, Gansu Province, with the Honggou section in the Yaojie area serving as its reference section (Wang Si’en and others, 1985).
Synonym: （窑街组）; Yaochieh Fm
Lithology and Thickness
The formation is composed of sandstones and shales, intercalated with coal beds, and is subdivided into four members in ascending order as follows: First member is composed of grey-white and yellow-brown conglomerates, intercalated with medium- and coarse-grained sandstones and poststones (=fine-grained sandstone), containing ferruginous and manganese bands and concretions, with a thickness of 39 m. Second member is composed mainly of grey-black and black mudstones and carbonaceous mudstones, intercalated with coal beds and powdery coal and poststones, with a thickness of 34 m. Third member consists mainly of grey-black and black mudstones, intercalated with siltstones, poststones and marls, with its upper part containing siderite bands, with a thickness of 94 m. Fourth member is composed largely of grey-green clays, intercalated with poststones and thin coal beds and coal seams, with a thickness of 71 m.
Relationships and Distribution
Lower contact
The formation is in a conformable contact with the underlying Daxigou Fm
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Xinhe Fm
Regional extent
The formation is distributed in the eastern segment of the Qilian Mts, including the Wangjiashan and Dashuitou areas of Jingyuan County, the Jiutiaoling Ridge of Wumei County, the Tanshanling Ridge and Datan area of Tiaozhu County, the Sishiming area of Yongdeng County, and the Yaojie Street of Lanzhou City, Gansu Province, as well as Minhe County of Qinghai Province. There are some differences in the lithology of the formation between various regions. In the Tanshanling, Datan and Sishiming areas, as well as in the Minhe Basin the lithology of the formation is similar to that of it found in the Yaojie area. As in other basins the rocks in the middle part of the formation are getting coarser in grains, with the oil shales and marls missing, while the upper and lower parts of the formation represent gritstones and conglomerates in most cases.
GeoJSON
Fossils
Except for the first member, all the other three members tend to yield abundant plant fossils, with its middle part yielding also bivalve and fish fossils. Among the plant fossils important members comprise Coniopteris hymenophylloides, Cladophylebis sp., Podozamites lanceolatus, Czekanowskia rigida, Baiers furcata, Phoenicopsis angustifolia and Elatocladus manchurica.
Age
Depositional setting
Additional Information